1. Field of the Invention
The present invention relates to a charged particle measuring apparatus for measuring the types and energy of charged particles in a field where a plurality of charged particles (e.g., electrons, protons, xcex1 particles, and so on) exist together, such as in space and in a space ship.
2. Description of the Related Art
Conventionally, charged particles have been measured for types and energy by using a telescope type measuring apparatus having a plurality of detectors in layers. In order to measure the total energy of a high-energy charged particle incident on the detectors, it has been considered necessary for the detectors to have sufficient thicknesses so that the total energy of the incident changed particle is absorbed within the detectors. For this reason, there have been developed xcex94E telescope type charged particle measuring apparatuses in which a plurality of detectors and absorbers are arranged in combination, and improved xcex94Exc2x7E telescope type charged particle measuring apparatuses. FIG. 9 shows a block diagram of a conventional xcex94E telescope type charged particle measuring apparatus which measures electrons, protons, and xcex1 particles for energy. FIG. 10 shows theoretical calculations of the relationship between the energy which charged particles lose to form electron-hole pairs in the detectors (hereinafter, referred to as loss energy) and the total energy of the charged particles prior to incidence (hereinafter, referred to as particle energy) for situations where the charged particles are incident on the xcex94E telescope type charged particle measuring apparatus shown in FIG. 9. FIG. 11 is a conceptual diagram showing the configuration of detectors in a conventional xcex94Exc2x7E telescope type charged particle measuring apparatus. FIG. 12 shows a block diagram of the conventional xcex94Exc2x7E telescope type charged particle measuring apparatus. With reference to FIGS. 9 and 10, description will first be given of the conventional xcex94E telescope type measuring apparatus.
In FIG. 9, the reference numeral 1 represents a charged particle, and 201-203 absorbers for absorbing the energy of the charged particle. The absorber 201 is made of aluminum of 0.1 mm in thickness. The absorber 202 is made of copper of 2 mm in thickness. The absorber 203 is made of tantalum of 2 mm in thickness. The reference numerals 204-207 represent detectors, each of which is a silicon semiconductor detector of 0.2 mm in thickness. The reference numerals 208 represent amplifying units, 209 a trigger generating unit, 210 a three-channel pulse-height discriminating unit, and 211 a data processing unit.
When the charged particle 1 is incident on the xcex94E telescope type charged particle measuring apparatus, the detectors 204-207 generate electron-hole pairs if the charged particle 1 passes therethrough or impinges thereon. The amplifying units 208 detect these electron-hole pairs and convert them into analog pulse signals proportional to the number of electron-hole pairs generated.
The electron-hole pairs generated by the detector 204 are converted by the amplifying unit 208 into an analog pulse signal for output. The output is applied to the three-channel pulse-height discriminating unit 210. The three-channel pulse-height discriminating unit 210 discriminates the incident charged particle among an electron, a proton, and an xcex1 particle. The result is output as an address 1 to the data processing unit 211.
Now, the method of discriminating a charged particle in the three-channel pulse-height discriminating unit 210 will be described with reference to FIG. 10.
In FIG. 10, the axis of ordinates on the left shows the loss energy of the incident charged particle 1 on a logarithmic scale in units of mega-electron volts (MeV). The axis of abscissas shows the particle energy of the incident charged particle on a logarithmic scale in units of MeV.
L1, L2, and L3 shown on the right axis of ordinates in FIG. 10 are 0.05 MeV, 0.4 MeV, and 6 MeV, respectively, which are values predetermined for discriminating the types of charged particles. The curves designated by S1-S4 are ones obtained from theoretical calculations of the relationship between the loss energy and particle energy of charged particles detected by the detectors 204-207, respectively. The curves are classified into three curve groups which represent the types of incident charged particles, namely, electron, proton, and xcex1 particle. If the loss energy of the charged particle concerned falls between L1 and L2, the incident charged particle is discriminated as an electron. If the loss energy of the charged particle concerned falls between L2 and L3, the incident charged particle is discriminated as a proton. If the loss energy of the charged particle concerned exceeds L3, the incident charged particle is discriminated as an xcex1 particle. When the charged particle is a proton, the rising parts of the curves S1-S4 lie in the electron area below L2. Charged particles detected in this area are discriminated as electrons even if they are protons. However, such occasions are extremely rare and will thus be left ignored. The same also holds for the rising parts of the curves S1-S4 when the charged particle is an xcex1 particle.
The output, or the analog pulse signal, converted by the amplifying unit 208 from the electron-hole pairs detected by the detector 204 is applied to the trigger generating unit 209. If the output applied exceeds a threshold value for noise distinction which is set in the trigger generating unit 209, the trigger generating unit 209 generates a trigger signal and applies the trigger signal to the data processing unit 211.
The three-channel pulse-height discriminating unit 210 contains the values of analog pulse signals corresponding to L1, L2, and L3 of FIG. 10 above. The three-channel pulse-height discriminating unit 210 compares the values of analog pulse signals corresponding to L1, L2, and L3 with the output, or the analog pulse signal, converted by the amplifying unit 208 from the electron-hole pairs generated by the detector 204, and thereby discriminates the type of the charged particle. As described above, the result is output as the address 1 to the data processing unit 211.
The detectors 205-207 generate electron-hole pairs when the charged particle 1 passes therethrough or impinges thereon. The amplifying units 208 apply analog pulse signals proportional to the number of electron-hole pairs to the data processing unit 211.
In response to the trigger signal from the trigger generating unit 209, the data processing unit 211 determines up to what detectors generate the analog pulse signals, based on the inputs of the analog pulse signals proportional to the number of electron-hole pairs generated by the detectors 205-207. Take, for example, a case where the discrimination of the charged particle 1 by the three-channel pulse-height discriminating unit 210 results in a proton, and the detectors 204 and 205 generate analog pulse signals while the detector 206 does not. From FIG. 10, it is determined that the particle energy of this proton falls within the range of 6.1 MeV, which is shown by the rising part of the curve S2 of the proton group, and 20 MeV, which is shown by the rising part of the curve S3 of the proton group (hereinafter, the sections of particle energy range will be referred to as energy channels). The result of determination is an address 2.
Using the address 1 and the address 2, or the output from the three-channel pulse-height discriminating unit 210 and the outputs from the amplifying units 208 of the detectors 204-207, the data processing unit 211 cumulatively adds the frequencies of occurrence of the events that charged particles are measured for the respective energy channels, with respect to each type of the charged particles. The frequencies are accumulated into memories of those addresses provided in the data processing unit 211. The contents of the memories are transmitted to the ground at regular time intervals to obtain data of the charged particles by type and by energy channel.
In this way, the types and particle energy of charged particles incident on the charged particle measuring apparatus can be measured by measuring the charged particles for loss energy.
As shown in FIG. 10, the energy for charged particles to lose in the detectors 204-207 decreases to the right. Then, where the charged particles are high in particle energy has the problem that protons can get into the electron area and xcex1 particles the proton area, causing errors in the distinction of the charged particles.
Besides, in this xcex94E telescope type charged particle measuring apparatus, the number of detectors determines the number of energy channels as described above. To increase the number of energy channels of charged particles, it is thus necessary to increase detectors and absorbers in number.
Now, a xcex94Exc2x7E telescope type charged particle measuring apparatus will be described with reference to FIGS. 11 and 12.
In FIG. 11, the reference numeral 1 represents a charged particle, 301 a xcex94E detector, 302 an Exe2x80x2 detector, and 303 an Erej detector. In FIG. 12, the reference numeral 1 represents a charged particle, 311-315 detectors, 316 amplifying units, 317 an adding unit (A), 318 an adding unit (B), 319 a 16-channel pulse-height discriminating unit, 320 an operating unit, 321 a four-channel particle discriminating unit, 322 trigger generating units, 323 a match detecting unit, and 314 a data processing unit.
When a charged particle is in a domain of relatively low energy, the energy dE for the charged particle to lose in moving inside a substance by a minute distance dx can be approximated as follows:
xe2x88x92dE/dxxe2x88x9dMZ2/Exe2x80x83xe2x80x83Eq. (1) 
Here, M is the mass of the charged particle, Z the charge of the charged particle, and E the particle energy of the charged particle. The equation (1) modifies into:
Exc3x97(xe2x88x92dE/dx)xe2x88x9dMZ2xe2x80x83xe2x80x83Eq. (2) 
Given that MZ2 on the right side has a value of 1 for a proton, the ratios to a deuteron, a triton, 3He, and 4He are 2, 3, 12, and 16, respectively. The value of Exc3x97(xe2x88x92dE/dx) on the left side of the equation (2) is determined from the observed data on the loss energy of the charged particle, thereby discriminating the type of the charged particle.
The xcex94Exc2x7E telescope type charged particle measuring apparatus shown in FIGS. 11 and 12 adopts the foregoing principle to discriminate charged particles and measure the energy channels of the charged particles.
In FIG. 11, the xcex94E detector 301 detects xe2x88x92dE/dx of the equation (2) (hereinafter, xe2x88x92dE/dx will be referred to as xcex94E) and the Exe2x80x2 detector 302 detects the remaining energy Exe2x80x2 (Exe2x80x2=Exe2x88x92xcex94E). On the condition that the incident of the charged particle makes the xcex94E detector 301 and the Exe2x80x2 detector 302 produce outputs and the Erej detector 303 produce no output, xcex94E+Exe2x80x2 equals to the particle energy E. The foregoing equation (2) thus modifies into:
(xcex94E+Exe2x80x2)xc3x97xcex94Exe2x88x9dMZ2xe2x80x83xe2x80x83Eq. (3) 
The value of (xcex94E+Exe2x80x2)xc3x97xcex94E of the foregoing equation (3) is determined and the ratio to that of a proton is used to discriminate the type of the charged particle.
The xcex94E detector 301 of FIG. 11 corresponds to the detector 311 of FIG. 12. The Exe2x80x2 detector 302 of FIG. 11 corresponds to the detectors 312-314 of FIG. 12. The Erej detector 303 of FIG. 11 corresponds to the detector 315 of FIG. 12. The amplifying units 316 and the trigger generating units 322 of FIG. 12 make the same operations as those of the amplifying units 208 and the trigger generating unit 209 of FIG. 9. Description thereof will thus be omitted here.
The output of the detector 311 past the amplifying unit 316 is applied as xcex94E to the adding unit (A) 317, the operating unit 320, and the trigger generating unit 322. The outputs of the detectors 312-314 past the amplifying units 316 are applied to the adding unit (B) 318. The output of the detector 312 past the amplifying unit 316 is also applied to the trigger generating unit 322. The output of the detector 315 past the amplifying unit 316 is applied to the trigger generating unit 322. The adding unit (B) 318 adds the inputs from the three detectors to determine the above-mentioned Exe2x80x2, and applies the output to the adding unit (A) 317. The adding unit (A) 317 adds the output xcex94E from the detector 311 and the output Exe2x80x2 from the adding unit (B) 318 to determine the particle energy xcex94E+Exe2x80x2, and applies the output to the 16-channel pulse-height discriminating unit 319 and the operating unit 320. The 16-channel pulse-height discriminating unit 319 discriminates the particle energy xcex94E+Exe2x80x2 in 16 levels. The result is output as an address 2 to the data processing unit 324.
The operating unit 320 performs an operation between the output xcex94E from the detector 311 and the output xcex94E+E from the adding unit (A) 317 to determine (xcex94E+Exe2x80x2)xc3x97xcex94E, and outputs the same to the four-channel particle discriminating unit 321. The four-channel particle discriminating unit 321 discriminates among an electron, a proton, an xcex1 particle, and other heavy particles based on the ratio of the value of (xcex94E+Exe2x80x2)xc3x97xcex94E to that of a proton. The result is output as an address 1 to the data processing unit 324.
When the analog pulse signals from the detectors 311 and 322 are applied to the match detecting unit 323 through the amplifying units 316 and the trigger generating units 322 as described above, the match detecting unit 323 judges the concurrence between the inputs from the detectors 311 and 312. If the two inputs are judged as being the trigger signals resulting from the incidence of the same charged particle on the detectors 311 and 312 and there is no trigger signal input from the detector 315, the match detecting unit 323 outputs a second trigger signal to the data processing unit 324. The data processing unit 324 performs data processing in response to the input of the second trigger signal.
Using the address 1 and the address 2, or the output of the four-channel particle discriminating unit 321 and the output of the 16-channel pulse-height discriminating unit 319, the data processing unit 324 cumulatively adds the frequencies of occurrence of the energy channels of charged particles with respect to each type of charged particle. The frequencies are accumulated into memories of those addresses provided in the data processing unit 324. The contents of the memories are transmitted to the ground at regular time intervals to obtain data on the charged particles by type and by energy channel.
In the foregoing circumstances, if the analog pulse signal from the detector 315 is applied to the match detecting unit 323 through the amplifying unit 316 and the trigger generating unit 322, the match detecting unit 323 outputs no trigger signal even when concurrence is observed between the two inputs from the detectors 311 and 312. The reason for this is that the presence of the analog pulse signal from the detector 315 indicates the penetration of the charged particle through the detector 314, in which case Exe2x80x2 cannot be determined.
Consequently, when charged particles have so high energy as to penetrate the detector 314, the foregoing principle of this xcex94Exc2x7E telescope type charged particle measuring apparatus is no longer applicable.
As described above, conventional xcex94E telescope type measuring apparatuses have the problems that the types of incident charged particles are difficult to discriminate when the charged particles have higher particle energy, and that the detectors must be increased in number when an increase is intended of the energy channels to discriminate. Conventional xcex94Exc2x7E telescope type measuring apparatuses have the problem that charged particles having so high energy as to penetrate the detectors cannot be measured. In addition, both types of measuring apparatuses have the problem that measurement cannot be continued in the event of a detector failure.
The present invention has been achieved to solve the foregoing problems. It is thus a first object of the present invention to discriminate the types of charged particles accurately and the energy channels precisely. A second object is to detect a failure of the charged particle measuring apparatus while conducting measurement, and even when a detector or the like suffers a failure, continue the measurement in a mode corresponding to the failure.
To achieve the foregoing first and second objects, claim 1 of the invention provides a charged particle measuring apparatus comprising a first detector, a second detector, and a third detector arranged in the direction of incidence of charged particles, the second detector consisting of a plurality of detectors, loss energy characteristics of respective types of charged particles to be measured being expressed in two-dimensional addresses with an output from the first detector as a first address and outputs from the plurality of detectors constituting the second detector as a second address, the loss energy characteristics of respective types of charged particles being measured based on the two-dimensional addresses and the presence or absence of output from the third detector, the apparatus further comprising: a second random access memory for counting the number of times charged particles are measured for loss energy at the two-dimensional addresses, the loss energy characteristics of respective types of charged particles to be measured being expressed in the addresses; a read only memory containing segment numbers respectively given to a plurality of segments sections along the loss energy characteristics of respective types of charged particles to be measured, the loss energy characteristics of respective types of charged particles being expressed in the two-dimensional addresses with respect to each of a plurality of modes, the plurality of modes setting combinations of the first through third detectors excluding any one or more detectors for situations where the detector(s) out of the first detector, and/or the second detector consisting of the plurality of detectors, and/or the third detector suffer(s) a failure; and a first random access memory for counting the number of times the charged particles are measured for loss energy under addresses shown by the segment numbers in the read only memory corresponding to the mode, wherein outputs from the first random access memory and the second random access memory are used to discriminate the types of charged particles and measure the energy thereof.
To achieve the foregoing first and second objects, the invention also provides the charged particle measuring apparatus, wherein: the read only memory contains a segment number corresponding to all the addresses other than those given the segment numbers in each mode; and the apparatus includes a random access memory for counting the number of times the charged particles are measured for loss energy under the segment number.
To achieve the foregoing first and second objects, the invention also provides the charged particle measuring apparatus, wherein a segment or a plurality of segments having the same segment number(s) regardless of whether or not a charged particle penetrates the second detector is/are divided into two addresses each, depending on the presence or absence of the output from the third detector.
To achieve the foregoing first and second objects, the invention also provides the charged particle measuring apparatus, wherein the plurality of detectors constituting the second detector are identical in thickness and material.